Apparatus for controlling rotation



June 27, 1939. H. A. SATTERLEE 2,163,632

APPARATUS FOR CONTROLLING ROTATION Filed Nov. 2, 1936 6 Sheets-Sheet 1l3 g u :2 15 I7 16 :9 e9

INVENTOR. Howe rd 4. if/fr/a e June 1939. H. A. SATTERLEE APPARATUS FORCONTROLLING ROTATION 6 Sheets-Sheet 3 Filed Nov. 2, 1936 FIG? -INVENTOR. Howe rd A 5 zffer ya] W 1 ATTORNEY.

June 27, 1939. A, sATTERLEE 2,163,632

APPARATUS FOR CONTROLLING ROTATION Filed Nov. 2, 1936 6 Sheets-Sheet 4 nDC.

FIG. 6

FIG. 9

INVENTOR.

ATTORNEY.

June 27, 1939.

FIG H H. A. SATTERLEE 2,163,632

APPARATUS FOR CONTROLLING ROTATION Fil e d Nov. 2, 1936 6 Sheets-Sheet 5INVENTOR. 7 HOWd/O ZHEr/ee Patented June 27, 1939 UNITED STATES PATENTOFFlCE Howard A. Satterlee, Needhani,

Mass., assignor to Submarine Signal Company, Boston, Mass,

a corporation of Maine Application November 2, 1936, Serial No. 108,853

8 Claims.

The present invention relates to a method and apparatus for controllingrotation. More particularly the present invention relates to a methodand apparatus for controlling the speed of rotation of a motor and to anapparatus for moving by means of a motor a certain device into a desiredposition from a remote point.

One object of the present invention is to provide a motor havingvariable speed characteristics. A further object of the presentinvention is to provide a power-braking device. Another object is toprovide an arrangement for the control of the rotation or other movementof a device into a desired position from a remote point. Other objectsof the invention will appear from the following description and thedrawings.

It has long been desired in a multitude of applications for electricmotors to have a motor control system whereby the motor speed can bevaried throughout a verywide range and at the same time have availablesubstantially full load torque. It has also been desired to haveavailable such a system which would give substantially constant speedthroughout the entire speed range with a varying load. The presentinvention provides a motor control system having the above desirablefeatures.

The present invention is also adaptable to the control of rotation ofany desired device from a remote point such as a signal hand or pointeror valve. In such cases the remote indicator or valve is set and movedaccurately with the movement of the operator's hand control and occupiesthe position chosen by the operator.

Heretofore the most accurate way of accom= plishing this has been bymeans of a hydraulic control arrangement. However, hydraulic devices areextremely expensive and a cheaper control system is very much desired.Electric motordrivm arrangements have also been used, but these havebeen open to a number of objections. They have not permitted asufliciently accurate and close setting of the indicator device and havebeen rather erratic in behavior in that it has not been possible toobtain a smooth flow of power to rotate the indicator device or valveespecially where large amounts of power may be required. Furthermore, ithas not been possible at a reasonable cost to obtain a variableoperating speed such that the speed of rotation increases automaticallyin relation to the amount of rotation desired.

The present invention will best be understood from the followingdescription with reference to the accompanying drawings in which Fig. 1is a schematic representation of the mechanical elements of the system;Fig. 2 is an elevation of an adjustable resistance device which is shownpartly in section in Fig. 1 and is employed in the modification shown inFig. 4; Fig. 3 is an elevation of the control wheel and scale of thearrangement shown in Fig. 1; Fig. 4 is a schematic wiring diagram of onemodification of the invention as applied particularly to the mechanicalarrangement shown in Fig. 1; Fig. 5 is a modification .of the systemshown in Fig. 4; Fig. 6 is a schematic wiring diaphragm of a variablespeed motor control according to the invention; Figs. 7, 8, 9, l0 and 11are schematic wiring diagrams of modifications of the invention asapplied to motor speed control; Fig. 12 is a schematic wiring diagram ofa modification of the invention for obtaining a power-braking effect;and Fig. 13 is a modification of the arrangement shown in Fig. 12.

Referring first to Fig. 6, a motor I for driving any desired piece ofmachinery is of the direct current type having an armature 8i, aseparately excitable field winding 82 connected across a source ofdirect current and a series field winding 83 which can be disconnectedfrom the circuit with the aid of the switch 95. The armature of themotor is in series with a source of alternating current and with theanode-cathode circuit of a vacuum tube 84 which is preferably of thegaseous electron discharge type of tube. The tube 84 is shown as havingan anode 85, a cathode 86 and a grid 81.

It will be understood, however, by those skilled in the art that afour-element tube can be used if desired in this modification as well asin those shown in the other figures of the drawings. The armature 8| isconnected into the circuit by means of the double-pole, double-throwrelay 85 having the operating coil 15 controlled by switch 88. The relay65 may be arranged so that when the switch 88 is open, the armature 81will be connected into the circuit in one direction while when theswitch 88 is closed, the armature will be connected into the circuit inthe opposite direction. Also in series with the anodecathode circuit ofthe tube 81 is a reactor 89 which is preferably of the saturable coretype and which can be shortcircuited by means of the switch 97. Apotentiometer 9|] placed across a source of direct current potentialprovides a positive potential for the grid of the tube 84 through theconductors 9|, 92 and 93 by way of the relay 65 and the armature 8|. Acurrent-limiting resistor 64 is provided in the grid circuit.

The operation of the system is-as follows: Assume that the switch 95 isclosed in its upper position. The motor is now arranged to have aseparately excited field providing a continuous magnetic flux. Since thegrid of the tube 84 is positive with respect to its cathode, assuming aposition of the adjustable potentiometer contact 96, as shown in Fig. 6,the tube 84 will permit current to flow through the anode-cathodecircuit and therefore through the armature 8| during the positive halfcycles of the alternating current supply. Since this current isuni-directional, the armature will commence to rotate in a givendirection, thereby generating a back E. M. F. in proportion to its speedof rotation.

, Since the armature 8| is in series with the grid cathode circuit ofthe tube, the back E. M. F. generated by the armature is in series withthe potential drop across the resistor 90 and the connections are suchthat the back E. M. F. will oppose the potential drop. As the motorspeeds up, the back E. M. F. will eventually become equal to or greaterthan the potential drop across the resistor 99 between its negativeterminal and the adjustable contact 98. When this point of motor speedis reached, the grid 81 will become negative, thereby preventing currentflow in the anode-cathode circuit of the tube 84. Such current flow willbe completely suppressed until the speed of the motor under its loadreduces sufiiciently to permit the grid 81 again to become suificientlypositive to permit current to flow in the anode-cathode circuit. It willbe evident that the speed of the motor armature thus depends upon thesetting of the potentiometer contact 96 and the magnitude of theimpressed direct current potential across the potentiometer as well asupon the magnitude of the generated back E. M. F. and of the appliedalternating potential in the anode-cathode circuit.

The reactor 89 is of especial advantage in smoothing out the operationat low motor speeds and with verylight loads, but at higher speeds orgreater load it is not necessary and is preferably shortcircuited orotherwise cut out ot the circuit for it tends to reduce the voltageacross the armature and hence the armature current. On the other hand,the reactor may be designed to have a relatively high reactance value atlow motor speeds and substantially no effect in the circuit at higherspeeds. These conditions apply to the reactors shown in the otherfigures as well as to that of Fig. 6. I

If, now, the switch 95 be moved to its lower position the field winding83 will be in series with the armature 8| whereby the motor will begiven compound motor characteristics. By proper adjustment of thewinding 83 the load speed characteristic of the system can be made veryclose to a straight line.

This system, as well as those in the other modifications, is inherentlyentirely free from hunting. Hence no special means to prevent huntingare required. My speed control system has, therefore, the greatadvantage of simplicity and low cost.

The modification shown in Fig. 7 is similar to that shown in Fig. 6 withthe exception of the use of a pilot generator to supply the potentialfor the control of the grid of the tube 84. In this case the armature 8|of the motor I has its shaft connected to the armature 98 of the pilotgenerator 99. A field winding I for this generator is continuouslysupplied with direct current. In series with the field winding 82 of themotor 1 there is provided a switch 94 while the field winding 83 may beconnected in series with the armature 8| by means of a switch 95 or itmay be disconnected from the circuit by means of this switch. Thereversing switch llll is in this figure shown as a manually operatedfour-pole, doublethrow switch but it will be understood that it may bearranged for relay operation in' a manner similar to that shown for theswitch 65 in Fig. 6. The reversing "switch llil is arranged so that whenoperated from one position to the other, it will reverse the connectionsto both the armature 8| and the'armature 98.

The armature 8|, it will be noted, is connected in series with thesource of alternating current, the reactor 89 and the anode and cathodeof the tube 84. The armature 98 of the pilot generator, on the otherhand, has one terminal connected to the cathode 86 and the other to thenegative end of the potentiometer 90. It is,

therefore, connected in series with the grid-' cathode circuit of thetube 84 and its polarity is adjusted to oppose the potential drop acrossthe potentiometer 98 between the contact 98 and the negative terminal.In this respect the armature 98 in Fig. 7 takes the place of thearmature 8! in Fig. 6.

The operation of the system is similar to that above described withreference to Fig. 6 with the exception that insteadof employing the backE. M. F. developed by the motor armature 8i for the control of the gridpotential of tube 84, the arrangement shown in Fig. 7 employs thevoltage developed in the armature 98 of the pilot generator for thispurpose. This has the advantage when using only the field winding 82 orwhen using both the field winding 82 and the series winding 93 that thevoltage employed for controlling the speed of operation of the motor canbe adjusted to any convenient value even though the alternating currentsupply is of a relatively high voltage and the armature winding 9! islikewise designed for such a high voltage. Furthermore, by using thepilot generator for the control of the grid of the tube in place of themotor back E. M. F. it is possible to use a. series connected motor,such as is illustrated by Fig. 7 when the switch 99 is open and theswitch 95 is in its lower position. Such a system has series motorcharacteristics but will nevertheless run at a constant speed asdetermined by the setting of the potentiometer contact 96.

The pilot generator is also necessary for the operation of themodifications shown in Figs. 8

to 11, inclusive.

In Fig. 8 a modification is shown whereby full wave operation isobtained. The alternating current source is connected to the primary ofa transformer M2 the extremities of whose secondary winding areconnected to the anodes of two electron tubes M3 and 604. The secondarywinding of the transformer is also provided with a center tap which isconnected through the reactor 99 in series with the armature 8i andthence to t e cathodes of each of the tubes 503 and H14. T e armature 98of the pilot generator 99 likewise has one terminal connected to each ofthe cathodes of these two tubes while the other terminal is connected tothe negative end of the potentiometer 90. In other respects the circuitarrangement is similar to that previously described with reference toFig. 7 and it will be understood hat a reversing switch and a motorseries field winding may also be employed in this modification ifdesired.

In operation when the polarity of the alternating potential is such asto make the anode oi tube I03 positive, current will fiow through thistube and through the motor armature. At this time, however, the anode oftube I will be negative so that no current can flowthrough this tube.However, when the alternating potential in the secondary of thetransformer reverses in the next half cycle, the anode of tube I04 willbecome positive permitting current to flow in that tube while the anodeof tube I03 will simultaneously be negative, preventing current flow.Thus the armature 0| of the motor will receive a current impulse in eachhalf cycle provided, oi course, that the respective grids are positiveto permit conduction.

The potential of the grids will be determined by the speed of the motor,which determines the voltage developed by the armature of the pilotgenerator, and the setting of the contact 96. When the speed of themotor is sufilciently low so that the difference between the pilotgenerator F. and that of the potentiometer between the negative terminaland the contact 96 is such as to make the grids of both tubessufllciently positive to permit conduction during the half cycles whenthe respective anodes are positive, the motor will receive currentimpulses during each half cycle. On the other hand, when the motor speed7 rises sufiiciently so that the difi'erence between the pilot generatorvoltage and that across the active portion of the potentiometer makesthe grids negative, no current will fiow through the motor. It will beunderstood that this condition may last for one half cycle or for anumber of cycles, depending upon the load conditions on the motor.

The modification shown in Fig. 9 provides for operation of the systemfrom a three-phase alternating current source. The three-phase supply isconnected to the extremities of three star-connected reactors I05, I06and I01, these three points also being connected to the anodes of thethree vacuum tubes I08, I09, IIO, respectively. The center of the Y isconnected by means of lead I I I to the reactor 89, the motor armatureII and thence to the cathodes of the three tubes. The armature of thepilot generator 99 likewise has one terminal connected to the cathodesand its other terminal connected to the negative end of thepotentiometer 90 as in the previous figures.

In the operation of this system the three tubes will, when their gridsare positive as determined by the speed of the motor and thepotentiometer setting, pass current successively as their respectiveanodes become positive as determined by the three-phase alternatingcurrent supply. The grids of the three tubes are controlledsimultaneously in the same manner as the grids of the tubes of Fig. 8described above. The modification of Fig. 9 has the advantage of evensmoother operation than Fig. 8 and furthermore makes possible the use ofa motor of larger power without increasing the capacity of the tubes orthe anode voltage.

Fig. 10 also shows an arrangement for driving the motor from athree-phase alternating current source but only two tubes I I2 and II 3are employed. These have their anodes connected to two terminals of thethree-phase source respectively, the third terminal being connected in aseries manner to the reactor 89 and the motor armature 8| and thence tothe cathodes of the two tubes. The pilot generator is connected to thegrid circuits of the tubes similarly as in Fig. 8. This modification islower in cost than that of Fig. 9 since it requires only two tubes andthe Y- connected reactors can be dispensed with. The motor powerobtainable with a given tube capacity and a given voltage is, however,less than that of Fig. 9. On the other hand, the arrangement does permitthe operation of the system from a three-phase source at a minimumequipment expense.

To obtain even greater power and smoother operation with the samecapacity of tube and the samevoltage the modification of Fig. 11 may beused. This figure is in effect a combination of Figs. 8 and 9f Thethree-phase supply is connected to the delta-connected primary of atransformer Ill having three separate secondaries, all having theircenter taps connected together to the conductor H5 and thence in aseries manner to the reactor 89, the armature BI and thence in amultiple manner to the cathodes of the six tubes II 5 to I20, inclusive.The extremities of the three secondary windings are each connected tothe anode of one of the tubes. The potential of the grids of all thetubes are simultaneously controlled by the difference between the pilotgenerator voltage and the drop across the active part of thepotentiometer 90 as determined by p the setting of the contact 96 as inthe other modifications. Thus, this system provides full wave,three-phase operation, being in eirect a combination of Figs. 8 and 9.

The modification shown in Fig. 12 is similar to that of Fig. 6 with theexception that the reversing switch is arranged not to reverse the motorbut to stop it abruptly, in effect a power-braking action. This isaccomplished by using a threepole, double-throw switch in place of thetwopole switch used in Fig. 6. The connections of the various elementsfor the upper two poles of the switch I2I in Fig. 12 are identical tothe two poles of the switch 65 in Fig. 6. The third pole of the switchIZI is arranged, however, so that when the switch is thrown to the leftposition in Fig. 12, the connections of the system will be the same asFig. 6, while when the switch is thrown to the right position, the gridof the tube 85 is directly connected to the negative end of thepotentiometer 90 instead of to the contact 96 as before.

For normal operation, therefore, the switch I2I will be closed in itsleft position, but if it is de sired to stop the motor quickly, theswitch will be thrown to the right position. The potential of the gridof the tube is then determined wholly by the back E. M. F. of the motor;but the connections of the'motor armature with respect to the anodecathode circuit of the tube have been reversed by the reversal of theswitch I2I, so that the current impulses flowing through the motorarmature are in a direction to oppose the motors continued motion in itsoriginal direction. It will, therefore, slow down extremely rapidly; butwhen it reaches the point of zero motion, the grid of the tube will havebecome zero since the motor back E. M. F. will also be zero.Consequently no further current impulses can flow through the motor andit remains at rest.

It will be understood by those skilled in the art that the modificationsemploying more than one tube can be arranged to be operated in the samemanner for quickly stopping the motor merely by providing an extra poleof the reversing switch, this being connected as in Fig. 12.

Where a pilot generator is employed, it will, of course, also benecessary to reverse the generator connections so as to provide positivegrid potential while the motor is still in motion.

An-application of the arrangement of Fig. 12 to a paper-making machineor newsprint machine or the like is shown in Fi 13. A paper band I22involved in the machine in question continuously passesover rollers 523and I24 driven by the motor I. Should the paper band I22 break, themotor will automatically be stopped. To obtain this resultautomatically, the paper band 322 is arranged to move between a lightsource i 25 beneath lens E2B'and the photoelectric cell H27, the latterbeing in series with the battery m, the switch I25 and the-relay coil830. The remainder of the system is the same as that shown in Fig. 12with the exception that the relay l3i has been substituted in place ofthe manually operated switch 826 of Fig. 12. Thus with the relay coili319 deenergized and the relay contacts in the position shown in Fig.13, the system is arranged to run normally to drive the roll i2 3 andconsequently the paper band 522 at a speed determined by the settting ofthe contact 96. Should, however, the photoelectric cell I21! becomeenergized by the breaking of the paper band 522, the switch 829 beingclosed, the relay l3 will be energized throwing the relay contacts tothe opposite positions, thus resulting in the same conditions as whenthe switch in Fig. 12 is thrown to the right. The motor i willconsequently rapidly come to rest.

If instead of an automatically stopping system, it is desired to have aremotely controlled system, the arrangement may be similar to that shownin Fig. 13 with the switch 929 open. The motor may then be stopped bythefclosing of switch E32, thereby energizing the relay 8%,

An application of my motor speed control system to a system forcontrolling from a remote point the position of some indicating devicesuch as, for example, a dial indicator, is shown in Figs. 1 to 5,inclusive. The electrical features of this arrangement are shown insimplest form in Fig. 4 which is in general similar to the arrangementof Fig. 6, while the mechanical parts of the system are shown in Figs.1, 2 and 3.

In the schematic arrangement shown in Fig. 1 the indicator i is mountedat the end of a shaft 2 in front of a dial 3 and rotated by means of amotor 7 through the reduction gear system 6 and t, the larger gear 6driving a shaft 2 at the position of the operators control. A gear i isfixed to the shaft 9 and meshes with gear Ii fixed to the shaft 82. Alsofixed to the shaft 62 is a dial 3, a front view of which is shown inFig. 3. There is also fixed to the shaft 9 a gear M which meshes withgear l5 fixed to the shaft I6 carrying an inertia mass I'l to preventtoo rapid a turning of a handwheel 8. At the end of the shaft 9 there isfixed a gear 48 forming a part of a differential system which includesalsothe idler gear IQ and the gear 20. The idler gear carrier is fixedto the end of the shaft 2! while the gears 20 and 39 are fastened toeach other but free to revolve on the shaft 2!. At the opposite end ofthe shaft 2| there is mounted a cam 12 carrying the arm 67 whose end isprovided with a roller a dapted to make contact with the resistancewindings Ill and II wound around an insulating ring fixed to theinsulating base 69.

An elevation of this variable resistance device is shown in Fig. 2 fromwhich it will be noted that each of the resistances l0 and II arecircular in shape and extend over approximately ninety degrees of are.This variable resistance serves to control the operation of the gaseouselectron tube 63, shown in Fig. 4, as will be described 36. The ratio ofgear 5 to gear 35 is the same as that between gears H and I0,respectively. The self-synchronous generator 36 drives theselfsynchronous motor 31 which, through gears 38 and 39 of a one to oneratio and the difierential system rotates the arm 61. In this actionthere is no tendency for the handwheel to be rotated by the motor 3'?since the load on the handwheel side of the differential is much greaterthan that on the potentiometer side.

The operation of the motor ii and its control will be evident from aconsideration of Fig. 4. In this figure the motor I is of thedirect-current shunt motor type having its field winding 52 separatelyexcited from a direct-current source. A series connected compoundingfield may also be used if desired. The gaseous electron tube 63 has itsanode-cathode circuit supplied with alternating current and contains thearmature 6! of the motor 1 in series with it. A relay E55 is provided,which is a double-pole, double-throw relay and serves to reverse theconnections of the armature M of the motor i. The potential applied tothe grid of the tube 553 is obtained from the direct current sourcethrough the curtate extremely slowly near the position of balance andwhen the handwheel is only very slightly displaced, while much fasterrotation is to occur when the handwheel is displaced agreater amount.For this purpose the resistance variation is made small near theposition of balance and is made to increase rapidly for greaterdisplacements of the resistance arm.

A convenient mechanical form or" the resistance device is shown in Fig.2. The variable resistance arm 57 is mounted on the shaft 25 in Fig. l.The contact arm 5? normally makes contact .with a conducting segment 68mounted upon a suitable disc of insulating material 69. side of thesegment 58 are the resistances l0 and H with which the arm $1 makescontact when it is moved to one 'side or the other of segment 68. A cam72 is also provided fixed to the shaft 28 so that it'rotates with thearm 6?. The cam On either x I2 is arranged so that the contacts 13, Idare open when the arm Bl engages the segment 68 as well as while itengages the resistance ll. On the other hand, the contacts 13, M areclosed while the arm 61 engages the resistance 10. When anode circuit inthe same direction, the motor armature will rotate in one direction orthe other, depending upon whether the arm 61 is in contact with theresistance I0 or with the resistance ll.

The outer ends of the resistances Ill and H are both connected to thepositive side of the source of direct current while the inner ends,namelythose adjacent to the segment 68, are connected together andthrough a high resistance to the segment 68. From their junction theyare also connected through the resistance 16 to. the cathode of tube 63.The grid cathode circuit of the tube thus can be traced from the grid ofthe tube through the resistance 64 to the arm 61. Then when the arm isin contact with segment 58, the circuit continues through resistances lland 16 to the cathode, and when the arm is in contact with theresistances ID or H, the circuit continues through a portion of therespective resistance to the resistances lli and the cathode of thetube. It will be noted that the resistances l0 and H are eachpotentiometers connected across a source of direct current, their outerterminals being positive and their inner terminals negative. Thus, asthe arm 61 is moved outward, away from the segment 68, along either ofthe resistances 10 or H, the grid of tube 53 becomes more and morepositive with respect to the cathode.

As soon as the grid of tube 63 becomes positive, the tube will becomeconductive and unidirectional current impulses will fiow in the anodecircuit through the armature 6| causing it to rotate. The rotation ofthe armature in the direct current field produced by the winding 62causes a back E. M. F. to be induced in the armature winding. Thearmature, it will be noted, is connected through the conductors l8 and19 across the terminals of the resistance 16 which is in the gridcathode circuit as above described.

The function of the resistance 16 is to prevent opening of the gridcircuit when the reversing relay operates. The back E. M. F. is thusimpressed across this resistance and is in the opposite direction to thegrid cathode potential supplied through the resistance I0 or H. As thearmature 6| speeds up under the influence of the anode current, the backE. M. F. builds up to a greater and greater value until it issufiiciently high to neutralize the grid potential supplied through theresistances l0 and 'l I and thereby cause the grid potential to fallbelow the criti cal potential and consequently to cut off conductionthrough the tube. Thereupon the armature 6|, no longer being suppliedwith current impulses, tends to slow down the back E. M. F.

consequently decreases to a point where it is no.

longer sufficient to neutralize the applied positive grid potential,whereupon the tube again becomes conductive. This phenomenon is repeatedand results in the armatures attaining a constant speed determined bythe setting of the arm 61 along the resistance III or H. It will beevident that not only at starting but also at all speeds full torque isavailable, the armature being supplied with current impulses justsuflicient in number to keep its speed at the value determined by thesetting of the resistance 56 and the back E. M. F. developed by thearmature. The operation in this respect is the same as that of Fig. 6.

As applied to the rotation of the indicating device or a valve, it hasalready been mentioned that the arm 61 is fixed to the shaft 2! ofFig. 1. Thus, when the handwheel 8 is displaced in order to change theposition of the indicating device I, the arm 61 will be moved onto oneor the other of the resistances II, II and will be moved along theresistance by an amolmt depending upon the amount of change of positionwhich is desired as indicated on the dial coupled to the handwheel 8.

The subsequent rotation of the motor I in turning the indicating deviceinto the desired position also brings about the rotation of theself-synchronous generator 36 and the self -syn chronous motor 31, whichthrough gears 38 and 39 operates to return the arm 61 towards thesegment 68 which will be reached when the indicating device has beenrotated into the proper position. When this position is reached, themotor stops.

Since the motor speed is dependent upon the position of the arm 51 onthe resistance II or H as explained above, it will be understood that asthe indicating device approaches the desired position and consequentlyas the arm 6! approaches the segment 68, the motor speed graduallyreduces, so that the indicating device comes to a smooth stop. If theresistances are suitably proportioned, thereis no tendency for it toovershoot the desired position since, as stated above, the system isnon-hunting. However, if it should overshoot, the motor will reverse atslow speed to return to the correct position. Extremely accuratesettings can be made with the added advantages of high speed for largeposition changes, low speed for small changes, substantially full torqueat all speeds; and at the same time the apparatus required is simple,resulting in low manufacturing and maintenance costs.

In order to keep the position of the dial B in reasonable correspondencewith the actual position of the indicating device, it may be desirableto place a limitation upon the speed with which the handwheel is turnedso as to give the motor time to set the indicating device into rotation.This is the function of the inertia weight H, shown in Fig. 1, althoughany other suitable device may be substituted for limiting the Speed atwhich the handwheel 8 can be turned, particularly at starting.

It will be evident that any desired sequence of fast or slow operationcan readily be obtained by suitably proportioning the steps into whichthe resistance means are divided and the manner in which the contactingarm is moved over them. This is true not only for the positioning systemjust described, but also for the variable speed motor systems describedwith reference to the other figures of the drawings. My invention may,for instance, be applied to the control of the driving motor for machinetools or the like with any desired sequence of fast, slow or reverseoperation or a sudden or gradual stop.

Itwill also be understood by those skilled in the art that themulti-tube arrangements of Figs. 8 to 11 may be used in place of thesingle tube shown in Fig. 4 for the positioning control.

The modification of Fig. 5 is identical with that of Fig. 4 except forthe insertion in the anodecathode circuit of a reactance 88, previouslymentioned with reference to Fig. 6. Such a reactance is a considerableadvantage in smoothing the operation at low motor speeds.

Having now described my invention, I claim:

1. A system for bringing to an abrupt stop an electric motor having anarmature and normal excitation means therefor comprising means forremoving normal motor armature excitation and means for energizing thearmature in reversed direction including a grid-controlled rectifieradapted to pass current through said armature and' means for applying tothe control grid a positive potential varying in direct proportion tothe motor speed.

2. A variable speed driving system including, in combination, a motorhaving an armature winding and a field winding, means for exciting thefield winding with direct current, a threeelectrode gaseous electrontube having anode,

cathode and grid electrodes and circuits for operatively connecting saidelectrodes, means for connecting said armature in series in theanodecathode circuit of said tube, means for applying an alternatingpotential to said anode-cathode circuit, means for reversing thedirection of connection of said armature in said circuit variableresistance means for applying a variable direct potential between thegrid and cathode of said tube, means operatively connected to saidvariable resistance for operating said armature reversing means andmeans for opposing the back E. M. F. generated in said armature againstsaid applied grid cathode potential.

3. A variable speed driving system comprising, in combination, anelectric motor having an armature winding and two-field windings, onebeing connected in series with the armature and the other being suppliedwith direct current, a grid-controlled rectifier, means for passing therectifier current through said armature and first field in series, meansfor applying to the control grid a positive potential adjustable inaccordance with the desired speed and means for opposing said potentialwith the back E. M. F. of said motor.

4. System for controlling the position of a body including a motoroperatively connected to said body to change the position thereof, saidmotor having an armature immersed in a continuous magnetic field andadapted to generate a back E. M. F. when in motion, a three-electrodegaseous electron tube having said armature in circuit with its anode,means for adjusting the'grid potential of said tube in accordance withthe desired change of position of said body, means for opposing saidgrid potential with said back E. M. F. and means controlled by themotion of said body for gradually returning said grid potentialadjusting means to its normal position as the desired position of saidbody is approached.

5. System for controlling the position of a body including a motorhaving an armature, a single grid-controlled rectifier, means forpassing the rectifier current through said armature, means for applyinga potential to the grid of a magnitude corresponding to the desireddegree of motion of said body comprising an adjustable potentiometeradapted to apply to said control grid a potential only slightly abovethe critical grid potential for small desired position changes andrelatively higher potentials for large desired position changes, meansfor opposing said applied potential by a potential varying in proportionto the motor speed and means operated by the motion of the body forreturning said potentiometer adjustment to its intial position as thedesired position of the body is attained.

6. System for controlling the position of a body including a motorhaving an armature immersed in a continuous magnetic field and adaptedto generate a back E. M. F. when in motion, a threeelectrode gaseouselectro'n tube having said armature in circuit with its anode, means forapplying a potential to the grid of said tube of a magnitudecorresponding to the desired degree of motion of said body, means foropposing the motor back E. M. F. to said grid potential and meansoperated by the motion of said body for reducing said grid potential asthe desired position of said body is attained.

7 A variable speed driving system for an electric motor having anarmature, including a gridcontrolled rectifier, means for passing therectifier current through said armature and means for controlling saidcurrent comprising means for.

applying a positive potential to the rectifier grid adjustable inaccordance with the desired speed, means for opposing said potential bya potential varying in proportion to the motor speed, and means forabruptly stopping the motor comprising means for suddenly reversing theconnections of the armature and simultaneously removing said positivegrid potential as well as said opposing potential and applying apositive potential to said grid varying in accordance with the speed ofsaid motor and becoming zero when said motor speed reaches zero.

8. A variable speed driving system comprising an electric motor having acommutator-type armature, an electron tube having anode, cathode andgrid electrodes, a source of alternating potential and circuits foroperatively connecting said electrodes including means for connectingsaid armature, said alternating current source and said anode andcathode in series relation to pass the tube current through saidarmature, means for applying a positive potential to said grid, meansfor opposing the same by the back E. M. F. of the motor, means foradjusting said positive potential in accordance with the desired motor,

